This invention relates to a process for producing resin impregnated fiber reinforced materials, and is particularly concerned with improved procedure for impregnating dry fiber reinforcement, e.g. carbon or graphite cloth, with a predetermined amount of resin, followed by final curing, to produce a resin impregnated reinforcement material having improved mechanical properties, while having reduced thickness and reduced resin content.
Most structural type composite parts, particularly those made for the aerospace industry, are fabricated from "B" stage resin impregnated woven cloth or tape fibers such as graphite. The resin is partially cured or "staged" to the desired consistency for tack and handling characteristics that will allow a later heat and pressure cycle to complete the fabrication process. This material is cut and laid up ply by ply, placed under a vacuum bag and the assembly is then placed in an autoclave and cured by heat and pressure to form the final "C" stage cured laminate.
The concept of impregnating dry fibrous materials such as woven cloth with a resin under vacuum conditions alone, followed by curing, does not compact the dry fiber preform sufficiently and produces a correspondingly heavy, thick high resin content lower strength product.
Illustrative of the prior art are U.S. Pat. No. 4,311,661, to R. J. Palmer and U.S. Pat. No. 4,942,013, to R. J. Palmer et al.
In U.S. Pat. No. 4,311,661 there is disclosed a vacuum resin impregnation process wherein vacuum pressure only is used to resin impregnate the fiber reinforcement layer and after impregnation, autoclave pressure and heat are applied for curing. The result is a resin-fiber composite which while compacted to some degree during curing under autoclave pressure, still retains a high resin content and such autoclave pressure does not reduce the thickness of the composite to the desired level.
U.S. Pat. No. 4,942,013 discloses a vacuum resin impregnation process, wherein a liquid resin/catalyst system is impregnated into a dry fiber reinforcement under vacuum pressure alone, and final curing of the resin takes place under vacuum pressure. Here also, the dry fiber preform is densified under vacuum alone to produce a relatively thick heavy composite of relatively high resin content, resulting in a composite having lower strength than desired.
Accordingly, it is an object of the present invention to provide an improved resin impregnation process for impregnating dry fiber reinforcement material, so as to produce a fiber resin composite having improved mechanical properties.
Another object is the provision of a process for resin impregnation of a fiber reinforcement so as to result in a cured composite of reduced thickness, and reduced weight and resin content.
Yet another object is the provision of an efficient process for fabrication of a resin-fiber composite by uniformly impregnating a fiber reinforcement material with a resin under conditions to reduce the thickness and resin content of the cured composite, and improving the mechanical properties thereof.
Other objects and advantages of the invention will appear hereinafter.